Net Absorption and Ruminal Concentrations of Metabolites in nonpregnant Dry Holstein Cows before and after Intraruminal Acetic Acid Infusion

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Abstract
Daily patterns of net absorption of various nutrients were defined and the effects of intraruminal infusion of acetic acid on concentrations of ruminal fluid and net absorption of various metabolites were assessed. These characateristics were measured in 3 nonpregnant, dry Holstein cows (491 kg) at hourly intervals for 24 h bfore and after 5 days of intraruminal infusion of acetic acid to provide energy equal to 10% of daily intake of metabolizable energy. Cows were fed a completely mixed, 60% corn silage, 40% grain supplement diet at maintenance intake; daily rations were split into 2 feedings. Net rates of absorption were greatest after feeding and least during early morning. Net absorption of all metabolites measured was similar for the 2 daily feeding intervals, indicating daily net absorption could be calculated from either feeding interval. Intraruminal infusion of acetic acid caused increased ruminal and plasma concentrations of acetate, increased net absorption of acetate, and almost a 2-fold increased loss of urea-N from plasma to the gut. Of the acetic acid infused 69%, was accounted for by increased net absorption of acetate. Ruminal fluid concentrations and net absorption of other volatile fatty acids were not affected by infusion of acetic acid. Net absorptions of NH3-N, L-lactate, and glucose likewise were not affected. Net absorption of volatile fatty acid and L-lactate was 43% of daily intake of metabolizable energy.